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Marine Fisheries Research - Age validation and research

Deacon Rockfish otolith collected in 2017
Deacon Rockfish otolith collected in 2017

The Oregon Department of Fish and Wildlife’s mission is to “protect and enhance Oregon’s fish and wildlife and their habitats for use and enjoyment by present and future generations.” The Marine Resources Program (MRP), a program unit within ODFW’s Fish Division, focuses on marine resources, habitat, and fisheries. To that end, MRP’s Fish Aging Project conducts specialized age reading, data management, and analysis. These data are used for age-structured stock assessments and other specialized studies of nearshore and shelf groundfishes off Oregon. The major goal of MRP’s Fish Aging Program is to produce reliable, precise, and accurate ages. We do this by applying standard age determination techniques and following accepted protocols for precision testing methods. This work is currently on-going.

Which species are aged each year is determined by the biennial federal stock assessment process as well as by ODFW researchers who identify existing data gaps that, once filled, offer increased accuracy and/or precision of age assignments.

We follow procedures outlined in The Manual On Generalized Age Determination Procedures For Groundfish. This document was produced by the Committee of Age Reading Experts (CARE), a cooperative effort between international and state and federal agencies dedicated to standardizing and improving age determination techniques and activities for eastern Pacific Ocean fish species. See http://care.psmfc.org/ for more information.

Age-structured stock assessments require thousands of ages to maximize the robustness of the assessment models. For most species, we use production methods involving the break-and-burn technique, whereby sagittal otoliths are scored across the core, snapped in half, lightly toasted over an alcohol lamp, and finally coated with mineral oil before being examined under a dissecting scope for age determination.

We use alternative structures like fin rays and vertebral centra to age Lingcod and rajids, respectively. These structures are embedded in epoxy resin and thin-sectioned using a low-speed diamond saw in order to distinguish annual marks for age estimation.

We also thin-section otoliths for smaller projects, including otolith microchemistry studies and investigations into effects of preparation technique on growth mark clarity.   

Data Analysis

After determining appropriate aging structures and techniques for the task at hand, an age is obtained for each structure. Approximately 20% of structures are re-read without knowledge of previously assigned age to obtain precision estimates (% agreement and average percent error).
In cases where the two ages do not match, a final age is determined by reading the structure a third time, with knowledge of the prior two reads. We construct von Bertalanffy growth curves to visualize the data and can examine annual growth differences by sex, year, and port.

Current and Future Projects

Otolith of 9-year-old Copper Rockfish prepared for ageing.
Otolith of 9-year-old Copper Rockfish prepared for ageing.

Break-and-burn aging of Black Rockfish (Sebastes melanops) and Copper Rockfish (Sebastes caurinus)

Black Rockfish are a semi-pelagic species that are the cornerstone of Oregon’s recreational fleet as well as an important component of Oregon’s non-trawl commercial fishery. Copper Rockfish have historically been a part of both the live-fish commercial fishery and recreational fishery throughout its range.

These ages will be used in future stock assessments (2021 for Copper Rockfish and 2023 for Black Rockfish).

Age validation of Cabezon (Scorpaenichthys marmoratus) using secondary ion mass spectrometry (SIMS) of O values in otoliths

O values of otolith aragonite are deposited at or near equilibrium with the ambient water composition. We will use high‐resolution sequential measurement of O values in an otolith, from core to margin, as a proxy for annual temperature cycles. A paired maximum and minimum in a series of sequential O values represent a winter and summer, respectively. Ages determined by counting the number of O maxima will be compared with ages determined from otolith growth zone counts in an attempt to validate annual periodicity.

Age Reading and Growth Publications and Information Reports

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